For the past 60 years, perovskite Pb(ZrxTi1-x)O3 (PZT) piezoelectric ceramics have dominated the commercial market of piezoelectric sensors, actuators and medical ultrasonic transducers due to their high dielectric, piezoelectric and electromechanical coupling factor properties. In addition, the properties of PZT piezoelectric ceramics can be further modified with different additives and/or dopants. In particular, PZT piezoelectric ceramics with compositions in the vicinity of a morphotropic phase boundary (MPB) that separates a rhombohedral phase from a tetragonal ferroelectric phase can exhibit anomalously high dielectric and piezoelectric properties. The high properties are the result of enhanced polarizability from the coupling between two equivalent energy states, i.e. between a tetragonal phase and a rhombohedral phase, which allows optimum domain reorientation during poling.
Numerous PZT formulations/compositions have been engineered for specific characteristics that enhance their use in many applications. For example, Tables I and II list the properties of commercially available soft PZT ceramics, and FIGS. 1 and 2 provide plots of dielectric permittivity and piezoelectric coefficient d33 versus Curie temperature (TC) for such materials. As shown by the data, polycrystalline materials with higher Curie temperatures generally possess lower dielectric and piezoelectric properties.
TABLE IPiezoelectric, dielectric and ferroelectricproperties of commercial PZT5A type ceramics.Prd33kptanδTC(μC/ECPZT5H(pC/N)(%)εr(%)(° C.)cm2)(kV/cm)TRS200HD14000.6620001.8340//3195STD23500.6318001.83503914.93295HD23900.6519001.83503912.0PIC25534000.6217502.0350//PIC15533600.6214502.0345//PKI50244250.6020001.5350//PZ2353280.5215001.3350//PZ2754250.5918001.7350//PZT5A164100.6218752.0370//PZT5A363740.6017002.0365//1TRS Technologies;2CTS;3PIceramic;4Piezo-kinetics;5Ferroperm;6Morgan.
TABLE IIPiezoelectric, dielectric and ferroelectricproperties of commercial PZT5H type ceramics.Prd33kptanδTC(μC/ECPZT5H(pC/N)(%)εr(%)(° C.)cm2)(kV/cm)TRS610HD16900.7039001.8210//CTS3203STD25500.6932502.02353710.6CTS3203HD26500.7038002.022539 8.0PIC15135000.6224002.0250//PIC15336000.6242003.0185//PKI53244900.6327002.0220//PKI55246000.6734002.2200//PZ2156400.6039801.6218//PZ2955700.6428701.6235//PZT5H166200.6034001.8200//PZT5H265900.6534002.5195//1TRS Technologies;2CTS;3PIceramic;4Piezo-kinetics;5Ferroperm;6Morgan.
It is appreciated that innovations in electronic devices have been the driving force for new developments in piezoelectric ceramics. In fact, and in order to meet the newly developed electromechanical devices, materials with Curie temperatures equivalent to heretofore developed materials but with higher dielectric and piezoelectric properties, and/or materials with similar dielectric and piezoelectric properties but higher Curie temperatures, are desired.
In addition to the above, the electromechanical coupling factor—the square of which is closely related to output power density—is known to be an important material parameter in ultrasonic transducer applications and the dielectric variation for prior art PZT based materials is relatively broad and on the order of 2000-8000 ppm/° C. Therefore, a new polycrystalline piezoelectric material with increased electromechanical coupling factor and reduced dielectric variation would also be desirable.